This application claims the priority of German patent document 100 61 186.9, filed Dec. 7, 2000, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a method for the galvanic deposition of nickel, cobalt, nickel alloys, or cobalt alloys in a galvanic bath, using an electrolyte containing nickel compounds or cobalt compounds, such as sulfates or sulfamates or chlorides. Such electrolytes for galvanic deposition are known, for example from the German patents DE 25 58 423 and DE 22 18 967 (U.S. Pat. No. 3,726,768); U.S. Pat. No. 2,470,775; and European Patent 0 835 335 (U.S. Pat. No. 6,036,833). For the deposition, at least one anode and at least one cathode of the bath is acted upon with periodic current pulses. Such methods with the help of current pulses are known from the state of the art, for example, from U.S. Pat. No. 2,470,775 and European Patent 0 835 335.
With such methods, nickel, cobalt, nickel alloys or cobalt alloys basically can be deposited in one galvanic bath. However, a special problem arises when the components, which are to be produced by such a deposition, should have particular mechanical properties, such as a specified strength or a specified ductility.
Such a problem arises particularly when the component that is to be produced is to be joined indissolubly later on, for example, by welding to other components. For this purpose, the ductility usually must meet certain minimum requirements, so that a welded joint can be realized between a galvanically produced nickel or cobalt layer or layer of any nickel or cobalt alloy and other components with sufficient strength and durability of the welded joint. However, if the ductility of the layer that is to be welded is too high, the strength of the corresponding layer is decreased. The corresponding layer, under some circumstances, no longer satisfies the specified requirements with regard to mechanical load-carrying capability. This is true particularly for components that are to be exposed to relatively high stresses such as to those that can occur in components of rocket engines. The thrust chambers of rocket engines, which consist essentially of components such as the injection head, combustion chamber and thrust nozzle, should be especially mentioned in this connection.
It has turned out that the methods, known from the art, cannot guarantee the necessary properties of the deposited layers of nickel or cobalt or of nickel alloys or cobalt alloys, which are an indispensable prerequisite for an indissoluble connection, especially by welding, of such a layer to other components, for example, those of an alloy based on iron or nickel.
It is therefore an object of the present invention to provide a method for the galvanic deposition of nickel, cobalt, nickel alloys, or cobalt alloys in a galvanic bath. At least one anode and at least one cathode of the bath are acted upon with periodic current pulses. Layers of nickel or cobalt or of nickel alloys or cobalt alloys can be produced, which can be connected indissolubly to other components and especially welded to other components.
This objective is accomplished according to preferred embodiments of the present invention.
In the case of a method for the galvanic deposition of nickel, cobalt, nickel alloys or cobalt alloys in a galvanic bath according to the present invention, an electrolyte is u d that contains appropriate nickel compounds or cobalt compounds, particularly sulfate or sulfamates or chloride. For the deposition, at least one anode and at least one cathode of the bath is acted upon with periodic current pulses, that is, a so-called plating method is used. Normally, a deposition body n which a layer of the appropriate material is to be deposited acts as cathode. Pursuant to the present invention, the IA/Ic ratio of the anode current density IA to the cathode current density IC is selected to be greater than 1 and smaller an 1.5. The charge ratio QA/QC=TAIA/TCIC of the charge QA, transported dun g an anode pulse of duration TA, to the charge QC, transported during a cathode pulse of duration TC, is between 30% and 45%.
It has turned out that the properties, especially with regard to the strength and ductility of the layer, which are necessary for an indissoluble connection of the deposited layer to other components, can be achieved only if such a ratio is selected. According to EP 0 835 335, on the other hand, it is proposed in particular, that an IA/IC ratio be selected that is at least 1.5. This document does not go into suitable parameter ranges for achieving a layer with the aforementioned properties. Furthermore, there is no mention there of selecting a suitable QA/QC ratio.
In preferred embodiments, the IA/IC ratio is between 1.2 and 1.45 and particularly between 1.3 and 1.4 and the charge ratio QA/QC=TAIA/TCIC is between 35% and 40% For these ranges of the parameters, particularly advantageous properties of the deposited layer can be noted, especially with regard to the strength and the ductility.
In order to achieve improved and uniform deposition of the layer on a deposition body, which in the final analysis is also to the benefit of the load-carrying capability of the layer over its whole extent, provisions can be made for the deposition. At least one contoured anode is used, the contour of which is adapted to the contour of the deposition body on which the nickel, the cobalt, the nickel alloy or the cobalt alloy is to be deposited. In particular, an almost constant distance between the anode and the deposition body can be achieved over almost all of the contour of the deposition body by this matching of the anode contour. This makes a uniform deposition possible.
If several anodes are provided in the bath, a contoured anode is used for at least one of the anodes that is closest to the deposition body. The effect of contouring the anode is greater for the anodes closest to the deposition body than for anodes further removed. Anodes without contouring, which are less expensive in some cases and can be used independently of the special shape of the deposition body, can therefore be used for the anodes that are further removed. Accordingly, by this suitable combination of anodes, which have and have not been contoured, an optimum can be achieved with respect to the quality of the deposition as well as the expenditure required for this purpose.
To form the contoured anode, a contoured container, for example, may be used that is permeable to the ions of the deposited nickel or cobalt or nickel alloy or cobalt alloy and which is filled with bodies of nickel, cobalt or a nickel alloy or a cobalt alloy. Special containers for such bodies are known from German patent DE 25 58 423 in the form of titanium or plastic baskets, which are filled with nickel pellets. However, contouring of the container is not disclosed in that document.
In principle, as an alternative to such containers, a solid electrode body that has at least a coating of the nickel, cobalt, nickel alloy or cobalt alloy, which is to be deposited, or that consists even of solid nickel, cobalt, nickel alloy or cobalt alloy, can also be used as a contoured anode.
During the deposition process, it may be necessary to selectively affect the deposition, which is to take place differently for different regions of the deposition body. This affecting may take place additionally or also alternatively to the aforementioned measure of the contoured anodes. For this purpose, provisions can be made so that the deposition body is shielded partially by current restrictors at least during a portion of the total duration of the deposition. During the time in which the regions are shielded, less deposition is achieved in the shielded regions than in the unshielded regions. Layer properties, especially the thickness of the layer, but also, optionally, the mechanical properties of the layer on the deposition body can be affected locally.
In particular, the current restrictors can be disposed in those regions of the deposition body in which deposition takes place preferentially. A layer growth, which is excessive in comparison to that in other regions, can be prevented in these regions and accordingly a more homogeneous layer growth can be realized over the whole of the deposition body.
Provisions can also be made to remove interfering extraneous elements or other suspended particles from the bath, in order to obtain the cleanest possible electrolyte solution. For this purpose, the electrolytes may be purified with the help of activated charcoal and/or of hydrogen peroxide at least before the deposition is commenced. In particular, for purifying the electrodes, 0.5 g/L to 5 g/L and especially 1 g/L to 3 g/L of activated charcoal and 0.5 mL/L to 3 mL/L and especially 1 mL/L to 2 mL/L of hydrogen peroxide are used before the start of the deposition.
However, in order to guarantee not only the cleanest possible electrolyte solution at the start of the process by such a purification, but also to maintain this purity as far as possible over the whole of the process, the electrolytes can be purified alternatively or also additionally during the deposition. For this purpose, in a preferred embodiment of the present invention, the electrolytes are filtered during the deposition, for example, through activated charcoal and extraneous elements are removed from the electrolytes by a selective bath. Such a selective bath corresponds to a galvanic bath, in which a selective deposition of extraneous elements and, with that, their removal from the electrolyte is accomplished by a selective control of the currents. The purified electrolyte, then ideally contains only the desired elements: (1) in the case of a nickel electrolyte, ideally only nickel or nickel alloys in the aforementioned compounds, and (2) in the case of a cobalt electrolyte, ideally only cobalt or cobalt alloys in the aforementioned compounds. The purified electrolyte is then returned to the galvanic bath.
In addition, the electrolyte can be circulated by at least one circulating pump and recycled into the bath through nozzles. The nozzles can be constructed and disposed in the bath, so that circulation of the bath is favored by the nozzles and/or flow of electrolyte directed on to the deposition body is achieved. In this case, not only do the nozzles fulfill the purpose of circulating and recycling the electrolyte into the bath, but also, due to the optimized nature of the recycling, the deposition process in the bath is favored since an optimum mixing and a selective supplying of an electrolyte, which is as pure as possible, to the deposition body is guaranteed at all times.
The method according to the present invention is suitable for producing different components, which later on are to be connected indissolubly with other components, for example, by welding. However, the method is also particularly suitable for producing components that are exposed to high stresses. Such components are, for example, rocket engines. In this connection, the method can be used for producing injection heads and/or combustion chambers and/or thrust nozzles for rocket engines. However, the method can also be used for other components, that are subjected to high stresses during later operation and therefore must have a sufficient strength, but nevertheless should have a sufficient ductility, such as, for example, bearing mechanical structures, components for baking ovens or similar arrangements with high thermal stresses, and the like. The achievable strength, as well as the ductility of the deposited layer, can be adjusted over a relatively wide range, as will be explained in greater detail in the text below, by a variation of the parameters of the method.
The present invention is also directed to a special galvanic bath for the galvanic deposition of nickel or nickel alloys or cobalt or cobalt alloys with an electrolyte, having
at least one contoured anode, the contour of which is fitted to the contour of a deposition body;
a device for triggering the anode and the cathode of the bath with periodic current pulses;
current restrictors for shielding the deposition body at least partly;
a filtering device for filtering the electrolyte; and
a circulating device for circulating the electrolyte, having at least one circulating pump and nozzles for recycling the electrolyte into the bath.
This galvanic bath can be used with the aforementioned method. However, the aforementioned method can also be realized in differently constructed galvanic baths, which are suitably adapted.
Other embodiments of this special bath can be accomplished by an appropriate adaptation to the method according to the present invention. For example, the at least one contoured anode may be constructed as a contoured container that can be filled with bodies of nickel or cobalt or a nickel alloy or a cobalt alloy.
Several anodes may be disposed in the bath, only the anode closest to the deposition body being constructed as a contoured anode. Of course, this also means that the remaining anodes have some contour. However, only the contour of that anode that is closest to the deposition body is fitted to the contour of the deposition body. In this connection, the contouring may extend only in one spatial direction, such as the longitudinal direction of the anode, or it may also extend in more than one spatial direction, for example, perpendicularly to the longitudinal direction.
Furthermore, the purifying device may comprise a filtering device, particularly an activated charcoal filter. Thus, suspended particles as well as undesirable extraneous elements can be removed from the electrolyte.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the present invention when considered in conjunction with the accompanying drawings